Technical Abstract:
Increasing atmospheric CO2 concentrations [CO2] are projected to have critical impacts on precipitation patterns, potentially leading to a dramatic increase in the frequency and duration of drought across the North American Corn Belt and other agriculturally relevant areas around the world (IPCC2007; USCSSP 2008). Plants respond to a myriad of abiotic and biotic stresses by activating signal transduction cascades to coordinate the physiological responses necessary for adaptation and survival. Abiotic stress affects some of the same hormonal signals stimulated by herbivory and can interfere with defense responses. The purpose of this study was to better understand the combined effects of elevated CO2 and severe drought on maize induced volatile production. Maize (Zea mays var. Golden Queen) was grown in environmentally controlled chambers at ambient (400 ppm) and elevated (800 ppm) [CO2]. Three week old plants were then subjected to seven days of drought by withholding irrigation. Maize leaf volatile production was not significantly altered by abiotic stress alone. We then further investigated the production of biotic stress induced volatiles by allowing Fall Armyworm caterpillars to feed on the fifth leaf for 24 hours. Despite the large amount of variation amongst plants there was significantly less volatiles produced by drought stressed plants and plants grown at elevated [CO2]. In order to eliminate any variation caused by differences in the amount of herbivory, we used a recently discovered Herbivory Response Peptide (HRP) to stimulate volatile production. Leaves from plants grown under different environmental conditions were excised and placed in an aqueous peptide solution for 16 hours before collecting volatiles. Drought stressed leaves treated with HRP emitted less volatiles than did HRP treated leaves from well-watered plants. Similarly, HRP treated leaves grown at elevated [CO2] emitted significantly less volatiles than HRP treated leaves grown at ambient [CO2]. In contrast to volatiles emitted, the internal leaf volatile concentrations were not significantly lower in drought stressed or elevated [CO2] leaves, nor were the transcript levels of caryophyllene (TPS23) and bergamotene (TPS10) terpene synthases significantly attenuated by the environmental stresses. Our data indicates that induced maize volatile emission may be hindered by physiological changes caused by climate change.